Method and apparatus for scan chain data management

ABSTRACT

Processing logic circuit has State Retention Power Gating logic circuit including at least two scan chains having different lengths and operable to collect state information about at least a portion of the processing logic circuit before the at least a portion of the processing logic circuit is placed from a first state into a second, different, state. The processing logic circuit includes a memory operable to store collected state information about the at least a portion of the processing logic circuit, and logic circuit operable to rearrange the collected state information data for scan chains shorter than a longest scan chain, to enable valid return of the collected state information data, for the scan chains shorter than a longest scan chain, to the at least a portion of the processing logic circuit when the at least a portion of the processing logic circuit returns to the first state.

FIELD OF THE INVENTION

This invention relates to computing systems in general, and inparticular to a method and apparatus for Scan Chain Data Management.

BACKGROUND OF THE INVENTION

In order to reduce power consumption of modern Integrated Circuits(ICs), many ICs now include the ability to turn off unused portions ofthe IC. However, to ensure the respective portion(s) of the IC are ableto quickly return to their fully operational state, particularly theexact logical state the portion(s) of the IC were in prior to them beingpowered down, certain state parameters are stored in a local memory.These stored state parameters are then loaded back into the ICportion(s), immediately after those portion(s) have been powered upagain, so that the respective portion(s) of the IC may carry on fromwhere they were before. A form of this process is often referred to asState Retention Power Gating.

The State Retention Power Gating (SRPG) technique is still one of themost aggressive power management techniques, because it allows thegating (i.e. turning off) of the power supply to the respectiveportion(s) of the IC, and thus saves power wastage/loss through leakagecurrents and the like, whilst still enabling the IC portion to get backinto its previous logical state.

Leakage currents (e.g. the leakage within the well of a transistor) areincreasing, as the dimensions of the transistors, and the like, thatform ICs get smaller with each iteration of the semiconductormanufacturing process.

Originally, SRPG was intended to be implemented using specially providedFlip Flop (FF) circuitry (i.e. retention latches), so that the statedata may be stored local to the respective logic circuit. However, asICs increased in size, hence requiring increasing amounts of local FF tobe provided in an IC, it became less and less efficient to store statedata these in retention latches. Thus, it became prevalent to save thestate data in a more centralised dedicated SRPG memory, by moving thestate data through the scan chains (i.e. test portions of the ICs undertest) and out for storage in the centralised SRPG memory.

SUMMARY OF THE INVENTION

The present invention provides a processing logic circuit for use in acomputing system, and a method as described in the accompanying claims.

Specific embodiments of the invention are set forth in the dependentclaims.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, aspects and embodiments of the invention will bedescribed, by way of example only, with reference to the drawings. Inthe drawings, like reference numbers are used to identify like orfunctionally similar elements. Elements in the figures are illustratedfor simplicity and clarity and have not necessarily been drawn to scale.

FIG. 1 shows a schematic diagram of a first discrete processor basedexample computing system to which the invention may apply;

FIG. 2 shows a schematic diagram of a second System on Chip (SoC)integrated multimedia processor based example computing system to whichthe invention may apply;

FIG. 3 shows an example of how invalid SRPG state data may be saved toSRPG memory in a storing cycle if there are no dummy units placed inshorter scan chains;

FIG. 4 shows an example of how the invalid SRPG state data as saved inFIG. 4 can be returned in a restoring cycle;

FIG. 5 shows an example rearrangement of the SRPG data stored in a SRPGmemory according to an example of the invention;

FIG. 6 shows an example of how the rearranged SRPG state data as savedin FIG. 5 can be returned, completely validly, in a restoring cycle;

FIG. 7 shows a schematic diagram of an example SoC computing systemaccording to an example of the invention;

FIG. 8 shows a flow chart of a portion of a method according to anexample of the invention;

FIG. 9 shows a more detailed schematic diagram of an example ofapparatus according to an example of the invention;

FIG. 10 shows a portion of a method as applicable to the apparatus ofFIG. 9, according to an example of the invention;

FIG. 11 shows a more detailed schematic diagram of an alternativeexample of apparatus according to an example of the invention;

FIG. 12 shows a portion of a method as applicable to the apparatus ofFIG. 11, according to an example of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Because the illustrated embodiments of the present invention may for themost part be implemented using electronic components and circuits knownto those skilled in the art, details will not be explained in anygreater extent than that considered necessary as illustrated above, forthe understanding and appreciation of the underlying concepts of thepresent invention and in order not to obfuscate or distract from theteachings of the present invention.

A problem with the existing approach of storing the state data in acentralised SRPG memory is that either the scan chains must all be ofthe same length, or some complexity must be added to the SRPG clockgating (i.e. sampling control/timing circuitry, usually in the form ofextra clock gating circuitry, i.e. leading to a much more complicatedclock tree design across the whole SRPG enable IC) or the shorter scanchains must be artificially lengthened (by adding further scan chainflip flops to all shorter scan chains), thereby making all the scanchains the same length (as the previous longest scan chain). Any whichway, extra logic circuits are added en-masse to the overall IC design,and therefore this leads to increased semiconductor die area use (whichadds costs, increases manufacturing error rate and can potentiallyincrease the IC's power draw in use, amongst other detrimental things).

In a typical IC design, for example a processor or System on Chip (SoC),and for many various reasons, up to 20-30% of scan chains can be shorterthan a predefined longest length of scan chain in use in the respectiveIC.

There is provided a processing logic circuit (e.g. IC—IntegratedCircuit) for use in a computing system, wherein the processing logiccircuit has a State Retention Power Gating logic circuit comprising atleast two scan chains having different lengths and operable to collectstate information about at least a portion of the processing logiccircuit before the at least a portion of the processing logic circuit isplaced from a first state into a second, different, state, saidprocessing logic circuit comprising a memory coupled to the StateRetention Power Gating logic circuit and operable to store a collectedstate information about the at least a portion of the processing logiccircuit, and logic circuit coupled to the memory and operable torearrange the collected state information data for scan chains shorterthan a longest scan chain within the at least a portion of theprocessing logic circuit, to enable valid return of the collected stateinformation data, for the scan chains shorter than a longest scan chain,to the at least a portion of the processing logic circuit when the atleast a portion of the processing logic circuit returns to the firststate.

The second, different, state may be either a state in which the at leasta portion of the processing logic circuit is in a different context oris in a lower power state (e.g. powered off).

The logic circuit coupled to the memory may comprise a processing unitwithin a same or another portion of the processing logic circuit that isto be placed into the second, different, state.

The processing unit may be a main central processing unit, CPU, oranother CPU within the processing logic circuit.

The rearrangement of the collected state data for scan chains shorterthan the longest scan chain may comprise moving invalid state datacollected during a SRPG state data storing process from one end of thedata structure comprising the state data to another end of the datastructure.

The collected state information data may be stored in a FIFO memory datastructure and the stored collected state information data may berearranged by placing invalid state information data for a shorter scanchain at an end of the FIFO memory that is loaded first back into the atleast a portion of the processing logic circuit.

The processing logic circuit may be a processor for a computing systemor a System on Chip.

The memory coupled to the State Retention Power Gating logic circuit maybe a part of the at least a portion of the processing logic circuit tobe placed from a first state into a second different state, and theprocessing logic circuit further comprises further logic circuit toreset the at least a portion of the processing logic circuit containingthe memory. The at least a portion of the processing logic circuit maycomprise any SRPG enabled module(s) or portion(s) of the processinglogic circuit.

There is also provided a method of scan chain data management inprocessing logic circuit, wherein the processing logic circuit has StateRetention Power Gating logic circuit comprising at least two scan chainshaving different lengths and operable to collect state information aboutat least a portion of the processing logic circuit before the at least aportion of the processing logic circuit is placed from a first stateinto a second, different, state, said method comprising collecting stateinformation about at least a portion of the processing logic circuitbefore the at least a portion of the processing logic circuit is placedfrom a first state to a second, different, state, and rearranging thecollected state information data for the scan chains shorter than alongest scan chain, to enable valid return of the collected stateinformation data for the shorter scan chains to the at least a portionof the processing logic circuit when the at least a portion of theprocessing logic circuit returns to the first state.

The second, different, state may be a state in which the at least aportion of the processing logic circuit is in a different context or isin a lower power state

The method may further comprise using a processing unit within a same oranother portion of the processing logic circuit that is to be placedinto the second, different, state.

The method may further comprise using a processing unit that is a maincentral processing unit, CPU, or another CPU within the processing logiccircuit.

The method may include rearranging the collected state data for scanchains shorter than the longest scan chain comprises moving invalid datacollected during a SRPG state data storing process from one end of thedata structure comprising the state data to another end of the datastructure.

The method may further comprise storing the collected state informationdata in a FIFO memory data structure and rearranging the storedcollected state information data by placing invalid state informationdata for a shorter scan chain at an end of the FIFO memory that isloaded first back into the at least a portion of the processing logiccircuit.

The method may further comprise collecting state information using amemory coupled to the State Retention Power Gating logic circuit that ispart of the at least a portion of the processing logic circuit to beplaced from a first state into a second different state, and resettingthe at least a portion of the processing logic circuit prior to or at asame time as rearranging the data. The method may further compriseapplying the method to any SRPG enabled module(s) or portion(s) of theprocessing logic circuit.

Thus, examples of the present invention provide a method and apparatusfor managing scan chain data, that uses rearrangement of the scan chaindata after the SRPG data has been loaded into the SRPG memory, so that,when read out again, it ends up in the right order, and providing thecorrect data to the respective portions of the IC (i.e. e.g. processinglogic circuit). Examples may provide correct SRPG operation withoutadding substantial extra circuitry to each (otherwise shorter) scanchain, or the clocking gating thereof.

The SRPG memory may be located in any suitable memory of (or locationin) the IC having SRPG capability, for example in the external systemmemory (e.g. DDR Ram, Rambus, or the like), or in a memory local (forexample formed on the same semiconductor die or on closely coupleddie(s) when the SRPG IC is formed as a system in package (SiP), or thelike) to the processing logic circuit for which the SRPG is provided.This local memory may take the form of a suitable amount of on-die DRAM(e.g. DDR RAM), Static RAM, or any functionally equivalent memorystorage means that may be incorporated on to a, or the same,semiconductor die(s) as the processing logic circuit to be provided withSRPG functionality.

The rearrangement may take into account the different length scanchains, so that the data, when read out back (i.e. restored) into thesame processing circuitry from which the state data was acquired, endsup with the state data in the correct order, and with valid datatherein. This is particularly for all scan chains shorter than thelongest scan chain in use.

The rearrangement may be carried out by a dedicated hardware module, orby the main, or any other CPU (central processing Unit) and/or corefound within the system, preferably also located on the samesemiconductor die (so that the latency until rearrangement starts is aslow as possible, and the actual speed of rearrangement may be as high aspossible, and the like).

The following examples will be disclosed in the context of a processorhaving SRPG functionality therein.

FIG. 1 shows a schematic diagram of a first discrete processor basedexample computing system 10 to which the invention may apply, forexample a desktop PC, laptop or the like.

The discrete processor based example (e.g. multimedia) computing system10 of FIG. 1 comprises a main CPU 110 (which is multicore in thisspecific example, but the invention is not so limited and may apply toany number of general processing cores within the processor 110), thatincludes a local (to the) main CPU cache memory 115 (for example level 1or 2 cache) for temporarily storing data for use by the CPU 110 duringits operation. The CPU 110 is also provided with SRPG circuitry 123,which is the circuitry that collects and stores (in the SRPG memory 124)the respective state information used within the processor 110 whenprocessing data according to data processing instructions and the like.The SRPG circuitry includes clock gating circuitry with links into therespective scan chains and the like, and is arranged to store the stateparameter data derived from the scan chains in the SRPG memory 124,which, as described above may be any form of suitable data storingmemory.

The CPU 110 may be connected to the rest of the computing system 10 byany suitable communications links. For example, by a common bus 120 (asshown), but may also be connected by a set of dedicated links betweeneach entity (e.g. CPU, memory, network adapter, etc) within thecomputing system 10, or a combination of shared buses for some portionsand dedicated links for others. The invention is not limited by theparticular form of communications links in use in respective portions ofthe overall computing system 10. Thus, entities within the computingsystem are generally able to send and/or receive data to and/or from allother entities within the computing system 10.

In the example shown in FIG. 1, the discrete processor based example(e.g. multimedia) computing system 10 further comprises a GPU/displaycontrol unit 130, potentially operatively coupled to a GPU memory 135either directly (as shown) or via a shared but (not shown). TheGPU/display control unit 130 may be a combined entity (as shown in FIG.1), including both the GPU and the necessary physical links (e.g. linedrivers, etc) to the display 140 (e.g. Liquid Crystal Display—LCD,plasma display, Organic Light Emitting Diode—OLED, or the like), or mayonly include the necessary physical links (e.g. line drivers, etc) tothe display 140, for example where there is no actual GPU, and insteadthe graphics are produced by the CPU 110 potentially in a dedicatedgraphics rendering mode or similar. This is to say, the discreteprocessor based example computing system 10 may not include the‘discrete’ graphics acceleration provide by having a GPU (where‘discrete’ here may not mean separation of the GPU from the CPU in termsof semiconductor die, but may instead mean there is separate dedicatedgraphic rendering capability). Where a GPU is present, the computingsystem 10 may further include a dedicated GPU memory 135, for use inprocessing graphics prior to display. Where such a GPU memory is notpresent, the GPU (or CPU in graphics mode) may use the external memory170 instead.

The GPU and/or display adapter 130 may be operably connected to thedisplay 140 via dedicated display interface, 145, to drive said display140 to show the graphical/video output of the discrete processor basedexample computing system 10. Examples of suitable dedicated displayinterfaces include, but are not limited to: HDMI (High DefinitionMultimedia Interface), DVI (Digital Video Interface) or analoginterfaces, or those functionally alike.

The discrete processor based example computing system 10 may furtherinclude one or more user input/output (I/O) units 150, for example, toprovide connection to, and therefore input from a touchscreen, mouse,keyboard, or any other suitable input device, as well as drivingsuitable output devices such as speakers, fixed function displays (e.g.9 segment LCD displays, LED flashing signal lights, and the like). Theuser I/O unit 150 may, for example, further include or comprise aUniversal Serial Bus (USB) controller, Firewire controller, Thunderboltcontroller or any other suitable peripheral connection interface, or thelike. The discrete processor based example computing system 10 may alsofurther include a network adapter 160, for coupling/connecting thediscrete processor based example multimedia computing system 10 to oneor more communications networks. For example, WiFi (e.g. IEEE802.11b/g/n networks), wired LAN (e.g. IEEE 802.3), Bluetooth, 3G/4Gmobile communications standards and the like. The computing system 10may also include any other selection of other hardware modules 180 thatmay be of use, and hence incorporated into the overall computing system10. The optional nature of these hardware modules/blocks 180 isindicated by their dotted outlines.

The computing system 10 may also include a main external memorysubsystem 170, operatively coupled to each of the other above-describedentities, for example, via the shared bus 120. In the context of thepresent invention, the external memory 170 may also include a portion(either permanently dedicated, or not, but otherwise assigned on bootup) for storing display data ready for display, known as a displaybuffer 175.

The invention is not limited by any particular form of external memory170, display 140, User I/O unit 150, network adapter 160, or otherdedicated hardware modules 180 present or in use in the future.

FIG. 2 shows a similarly capable computing system to FIG. 1, except thatthe computing system is formed as a SoC computing system 200, i.e.formed predominantly as a highly integrated multimedia/applications SoCprocessor 111. In such a situation, more of/most of the overall systemis formed within the same IC package (e.g. formed from two or moreseparate silicon dies, but suitably interconnected within the samepackage) and/or formed on the same singular integrated circuitsemiconductor die itself. However, in this case, some portions of theoverall computing system 200 may still be formed from other discreteentities. This form of multimedia computing system is used more often inthe portable and/or small form factor device use cases, for example, inthe form of laptops, tablet computers, personal media players (PMPs),smartphones/feature phones, etc. However, they also find use in otherrelatively low cost equipment areas, such as set top boxes, internetappliances and the like.

The majority of the SoC implemented multimedia computing system 200 isvery similar to, or indeed the same as for FIG. 1, therefore they usethe same references, and they act as described above (e.g. networkadapter 160, User I/O 150, etc). This includes the SRPG circuitry,including clock gating circuitry and circuitry that links into the scanchains, arranged for collection of the state parameter data.

However, there are some potential key differences. For example, the SoC111 may have its own internal bus 112 for operatively coupling each ofthe entities on the single semiconductor die (again, a shared bus isused in this example, but instead they could equally be one or morededicated links, or more than a single shared bus, or any otherlogically relevant/suitable set of communications links) to allow thedifferent entities/portions of the circuit (i.e. integrated entities—CPU110, Other CPU 131, etc) of the SoC to communicate with each other. ASoC multimedia processor 111 may incorporate more than one CPU foruse—thereby allowing multi-processor (e.g. core) data processing, whichis a common approach to provide more processing power within a givenpower (i.e. current/voltage draw/etc) envelope, and without having tokeep on increasing CPU operating frequencies. Due to having multipleCPU's on the same semiconductor die, there may be provided some form ofshared cache—e.g. shared L2 or L3 cache 113. This shared cache may stillbe “locked” to a subset of cores/PUs, i.e. only provided for use/accessby that subset of cores. The SoC based computing system 200 may includeother IP block(s) 132, dependent on the needs/intended uses of theoverall system 200, and how the SoC designer provides for thoseneeds/intended uses (e.g. whether he opts to provide dedicatedprocessing resources for a selected operation, or whether he just relieson a general processor instead). In the example of FIG. 2, there is alsoincluded a Direct Memory Access (DMA) unit 134, to allow direct accessto the external memory 170, and especially, in the context of thisinvention, the external memory display buffer 175. Another difference toFIG. 1 is the provision of separate GPU 116 and display controller 130′(the use of indicating a different form of display controller, i.e. inthis case without GPU).

In FIG. 2, there are two different example internal SoC graphicsub-system setups shown, but the invention is not so limited. Theseprimarily differ in how the respective graphics entities (CPU 110, GPU116, etc) communicate with each other.

For example, the first may involve the CPU 110 (when operating in someform of (dedicated) graphics mode) or GPU 130 communicating via theinternal on-die shared bus 112, particularly including the displaycontrol communications portion, 129′, i.e. the portion coupling thedisplay control unit 130′ to the shared bus 112. The other method may bevia a dedicated direct communications link, e.g. link 129 between, forexample, the GPU 116 and display control unit 130′ (a similar directcommunications link is not shown between the CPU 110 and display controlunit 130′, but this form may equally be used where there is no GPU inthe SoC). In the example shown, the display control unit 130′ and GPU116 are integrated onto the same SoC multimedia processor 111, but mayequally be formed of one or more discrete unit(s) outside of the SoCsemiconductor die, and which is connected by some suitable dedicated orshared interface (not shown).

Regardless of how the CPU/GPU is connected to the display control unit130′, they may also be operatively coupled to the display buffer 175,for example located in the external memory subsystem 170. This so calledexternal memory based display buffer 175 is accessible, in the exampleshown, via the internal shared bus 120, and the DMA unit 134 connectedthereto. In this way, the display data is communicable to the display140 via the display control unit 130′ under control of the CPU 110and/or GPU 116. The display buffers may also be included in the displayadapter (not shown). Also, it will be appreciated that other suitabledirect or indirect connections between the respective entities involvedin rendering the display may be used, depending on the particulardisplay driver circuitry configuration in use.

FIG. 3 shows an example of how SRPG state data may be saved to SRPGmemory in a storing cycle if there are no dummy units (e.g. extraflip-flops) added to the otherwise shorter scan chains, using asimplistic example with only two scan chains of different lengths. Thereis shown a first scan chain 401 of a first (longer) length, in thisexample being 8 units in length, and a second scan chain 402 of shorterlength (in this example, 6 units long). When the two scan chain statedata is clocked into the SRPG memory 124, in the usual way, there isformed an un-rearranged SRPG memory data set 410. Here, it can be seenthat the final two cycles of the SRPG data loaded into SRPG memory forthe shorter scan chain's results in invalid data, because that shorterscan chain 402 does not have valid state data to pass to the SRPG memoryfor those final two cycles (i.e. for the number of cycles by which thescan chain is shorter than the longest scan chain in use in the SRPG).

FIG. 4 shows an example of how the SRPG state data as saved in FIG. 4can be returned in a restoring cycle, and hence cause an invalidreturned state 402B for the shorter scan chain, whilst a valid state isreturned to the longer scan chain 401A. Here, because the scan chainstate data stored in the SRPG memory is restored back into therespective scan chain by circularly clocking the data back in to therespective scan chain, and this occurs in lock step across all the scanchains, and the state data is clocked back into the scan chains untilthe longest scan chain is suitably restored, the final two portions ofthe shorter scan chain now have the invalid data restored therein. Thisis because, without some timing complexity included for the restoreprocess/apparatus, or the insertion of dummy scan chain units, the validscan data for the shorter scan chain simply cycles back out for theclock cycles that are in excess of the number of restoring clock cyclesrequired for the shorter scan chain. This is to say, the shorter scanchains have valid data at the point in time when the number of restoringclock cycles equals the number of units in the shorter scan chain, butthere are still a number of further restoring clock cycles going tohappen (since the SRPG data is clocked back to the scan chains inlockstep), which results in the invalid data at the end of the SRPGmemory 124 for the shorter scan chain being loaded in to the shorterscan chain.

FIG. 5 shows an example rearrangement of the SRPG data stored in a SRPGmemory according to an example of the invention, so that there is noneed to include dummy scan chain units (e.g. flip-flops) for the shorterscan chains, or include the further complexity in the clock gatingcircuitry, e.g. the insertion of “dummy” clock gating signals, or thelike. Put simply, the scan chain state data for the shorter scan chaincan be re-arranged 601, after the scan state data load-in process intothe SRPG memory 124 is complete, to form rearranged scan chain statedata 620. This rearrangement 601 is carried out so that the invalid datacomes (out) first for the shorter scan chain during the restoring cycle.For example, for a case where the scan chain data is loaded in to andout of a FIFO (First In First Out) style memory/data structure (as shownin the Figures), this rearrangement 601 may comprise moving the invaliddata so that it is located at the front of the FIFO memory portion usedfor storing the state data for the shorter scan chains (i.e. it is thefirst data to come out of the FIFO memory). However, if a different formof data structure for storing the SRPG data is used, e.g. LIFO, adifferent rearrangement may be applied. The SRPG data rearrangement 601may be carried out by any suitable processing unit within the computingsystem, for example the main CPU or another CPU therein, or may becarried out by some suitable relatively simple and reusable extraprocessing logic circuit designed into the computing system, and whichmay be utilised by any and all shorter scan chains, thereby producing asaving on semiconductor die area compared to including a suitable numberof dummy scan chain units (for example flip-flops) into the shorterchains, or more complex scan chain data clocking (i.e. timing) circuitryfor each of the shorter scan chains.

The rearrangement may be viewed as enabling the valid return of thecollected state information data to the at least one portion of theprocessing logic circuit that enters the different state.

FIG. 6 shows an example of how the rearranged SRPG state data as savedin FIG. 5 can be returned, completely validly, in a restoring cycle.Here, the longer scan chain has returned to it completely valid data401A, but so has the shorter scan chain 402A. This has occurred, becausethe invalid data is read out of the SRPG memory 124 first, and returnedto the shorter scan chain, but is subsequently flushed out by the validdata, as the scan chain restore process continues for the requisitenumber of clock cycles to cover the longer scan chain.

FIG. 7 shows a more detailed schematic diagram of an example SoCcomputing system according to an example of the invention. This exampleis largely the same as shown in FIG. 2, except that there is a modifiedSRPG circuit 123′, to thereby provide a modified SoC multi-mediaprocessor 111′. The modified SRPG is one example implementation of theinvention, in that the modified SRPG circuit can be arranged tore-arrange the state data in the SRPG memory 124 as described above.However, other more specific implementations are envisaged, as describedbelow. The invention may also be implemented as tangible andnon-transitory software code, for execution on a general processor unit,such as the main CPU and/or an other CPU in the computing system, whereapplicable.

FIG. 8 shows a flow chart of a portion of a method according to anexample of the invention. The method may start at 910 and immediatelydetermine whether to move to a different state (e.g. power down, i.e.place into a lower power state, which may usefully involve the saving ofstate data—but the invention may also be applied to context changes aswell) at least a portion of the overall IC, thereby instigating thesaving of the state data for at least that one portion of the IC. Theportion to be placed into a different state, e.g. the lower power state,may be any size, up to and including the whole of the IC to which theinvention is applied. Multiple, smaller portions may also be put intothe different state, e.g. a lower power state, i.e. the invention is notlimited to the form or extent of SRPG in use, for context changes and/orpower saving techniques. If no portion of the IC is to be placed into alower power state (i.e. a NO 925 response decision), then the methodproceeds with processing as normal 930 and the method ends 960. If thereis at least one portion of the IC put into a different state, e.g. beingpowered down (i.e. a YES, 927 response decision), then the methodproceeds to save the state data largely in the usual way 940, butwithout using any dummy units or clock gating changes. Then the methodre-arranges the data in the, for example, SRPG memory 950.

FIG. 9 shows a more detailed example of a simple use-case for apparatusaccording to an example of the invention, for example where theimplementation in use stores the SRPG data in another module entirely(i.e. not a module that will be power gated, in this e.g., the on-dieRAM). The apparatus according to this example includes the powergate-able portion, e.g. module 1010, which itself includes, for example,a SRPG DMA circuit 1020. The SRPG DMA circuit 1020 is operable to movethe state data from the scan chain for the respective module 1010 intothe, for example, on-die SRPG memory 124, via the multiplexer 1030. Thismultiplexer 1030 provides access to the respective portion of the SRPGmemory 124, to either the SRPG DMA module (so that the SRPG DMA modulecan load the state data into the SRPG memory 124), or to the main CPU110—so that the CPU can carry out the afore-mentioned data rearrangement(according to one example of the invention). There is also shown indotted outline (to show the optional nature of this embodiment), afurther multiplexer 1031, which may be used to select access to theon-die memory by another CPU, e.g. other CPU 131, which may insteadcarry out the rearrangement of the stat data in SRPG memory 124. Thisform, i.e. using a further CPU selection means 1031, may be used inembodiments having more than one CPU in particular, so that the methodmay be applied to all CPUs (e.g. the main CPU can rearrange the SRPGdata for an other CPU 131, while the other CPU 131 can rearrange datafor the main CPU, etc, when each uses SRPG, respectively).

FIG. 10 shows a portion of a method as applicable to the exampleapparatus of FIG. 9. The method comprises (once a SRPG technique isdecided to be applied) the SRPG DMA circuit 1020 loading the scan chaindata 940, e.g. from the scan chain flip-flops, into the SRPG memory 124,followed by a CPU (e.g. main CPU 110 or other CPU 131 of FIG. 9)re-arranging the scan chain data 950 in the SRPG memory 124, and oncethe respective portion of the IC to which the scan chain relates isre-enabled (e.g. changes back to a first state), the respectivere-arranged scan chain data is loaded back into the state flip-flopsfrom the SRPG memory 124.

FIG. 11 shows a more detailed alternative example of apparatus accordingto an example of the invention, where the memory is within the samemodule that is undergoing SRPG. This time, there is only one CPU shownconnected through the multiplexer 1030, for clarity (but equally, morethan one could be used, as shown in FIG. 9). The most relevantdifference here is that even the SRPG memory 124 may be within the powergated module, but this is still a possible example implementation of theinvention because a reset state of the module or portion having the SRPGmemory 124 in most cases still allows basic functionality such as accessto the local memories. As will be appreciated, the SRPG memory maycomprise a plurality of smaller memories, i.e. a separate SRPG memoryfor each SRPG enabled module/unit/portion of the IC.

FIG. 12 shows a portion of a method as applicable to the apparatus ofFIG. 11, according to an example of the invention. This method islargely the same as shown in FIG. 10, except there is the additionalstep of resetting the gate module, 1310, which still allows access tothe (local) SRPG memory 124.

Thus, example embodiments of the invention provide an effective yetsimple to implement method and apparatus to enable SRPG scan chain datafor a plurality of scan chains of different length to be stored to aSRPG memory (local or external to the SRPG enabled module(s)/portion(s)of an IC, or indeed local or external to the SRPG enabled overall IC),all without requiring the use (i.e. having to include onto thesemiconductor die) of dummy flip-flops in the scan chains, in order tomake them all the same length, or more complexity in the clock gatingcircuitry, for example for generating ‘dummy’ cycles, or the like, whichcomplicate the clock gating tree design.

Example portions of the invention may be implemented as a computerprogram for a computing system, for example multimedia computing system,or processor therein, said computer program for running on themultimedia computer system, at least including executable code portionsfor creating digital logic circuit that is arranged to perform the stepsof any method according to embodiments the invention when run on aprogrammable apparatus, such as a computer data storage system, disk orother non-transitory and tangible computer readable medium. For example,examples of the invention may take the form of an automated IntegratedCircuit design software environment (e.g. CAD/EDA tools), used fordesigning ICs and SoCs in particular, that may implement theaforementioned and described SRPG data rearrangement invention.

A computer program may be formed of a list of executable instructionssuch as a particular application program and/or an operating system. Thecomputer program may for example include one or more of: a subroutine, afunction, a procedure, an object method, an object implementation, anexecutable application, an applet, a servlet, a source code, an objectcode, a shared library/dynamic load library and/or other sequence ofinstructions designed for execution on a suitable computer system, suchas an Integrated Circuit design system.

The computer program may be stored in a non-transitory and tangiblefashion, for example, internally on a computer readable storage mediumor (after being) transmitted to the computer system via a computerreadable transmission medium. All or some of the computer program may beprovided on computer readable media permanently, removably or remotelycoupled to a programmable apparatus, such as an information processingsystem. The computer readable media may include, for example and withoutlimitation, any one or more of the following: magnetic storage mediaincluding disk and tape storage media; optical storage media such ascompact disk media (e.g., CD-ROM, CD-R, Blueray, etc.) digital videodisk storage media (DVD, DVD-R, DVD-RW, etc) or high density opticalmedia (e.g. Blueray, etc); non-volatile memory storage media includingsemiconductor-based memory units such as FLASH memory, EEPROM, EPROM,ROM; ferromagnetic digital memories; MRAM; volatile storage mediaincluding registers, buffers or caches, main memory, RAM, DRAM, DDR RAMetc.; and data transmission media including computer networks,point-to-point telecommunication equipment, and carrier wavetransmission media, and the like. Embodiments of the invention are notlimited to the form of computer readable media used.

A computer process typically includes an executing (running) program orportion of a program, current program values and state information, andthe resources used by the operating system to manage the execution ofthe process. An operating system (OS) is the software that manages thesharing of the resources of a computer and provides programmers with aninterface used to access those resources. An operating system processessystem data and user input, and responds by allocating and managingtasks and internal system resources as a service to users and programsof the system.

The computer system may for instance include at least one processingunit, associated memory and a number of input/output (I/O) devices. Whenexecuting the computer program, the computer system processesinformation according to the computer program and produces resultantoutput information via I/O devices.

In the foregoing specification, the invention has been described withreference to graphics overlay data examples of embodiments of theinvention. It will, however, be evident that various modifications andchanges may be made therein without departing from the broader scope ofthe invention as set forth in the appended claims. For example, themethod may equally be used to compress data that is not used as much assome other data.

The terms “front,” “back,” “top,” “bottom,” “over,” “under” and the likein the description and in the claims, if any, are used for descriptivepurposes and not necessarily for describing permanent relativepositions. It is understood that the terms so used are interchangeableunder appropriate circumstances such that the embodiments of theinvention described herein are, for example, capable of operation inother orientations than those illustrated or otherwise described herein.

The connections as discussed herein may be any type of connectionsuitable to transfer signals from or to the respective nodes, units ordevices, for example via intermediate devices. Accordingly, unlessimplied or stated otherwise, the connections may for example be directconnections or indirect connections. The connections may be illustratedor described in reference to being a single connection, a plurality ofconnections, unidirectional connections, or bidirectional connections.However, different embodiments may vary the implementation of theconnections. For example, separate unidirectional connections may beused rather than bidirectional connections and vice versa. Also, aplurality of connections may be used, or replaced with a singleconnection that transfers multiple signals serially or in a timemultiplexed manner. Likewise, single connections carrying multiplesignals may be separated out into various different connections carryingsubsets of these signals. Therefore, many options exist for transferringsignals.

Each signal described herein may be designed as positive or negativelogic circuit. In the case of a negative logic circuit signal, thesignal is active low where the logically true state corresponds to alogic circuit level zero. In the case of a positive logic circuitsignal, the signal is active high where the logically true statecorresponds to a logic circuit level one. Note that any of the signalsdescribed herein can be designed as either negative or positive logiccircuit signals. Therefore, in alternate embodiments, those signalsdescribed as positive logic circuit signals may be implemented asnegative logic circuit signals, and those signals described as negativelogic circuit signals may be implemented as positive logic circuitsignals.

Furthermore, the terms “assert” or “set” and “negate” (or “deassert” or“clear”) are used herein when referring to the rendering of a signal,status bit, or similar apparatus into its logically true or logicallyfalse state, respectively. If the logically true state is a logiccircuit level one, the logically false state is a logic circuit levelzero. And if the logically true state is a logic circuit level zero, thelogically false state is a logic circuit level one.

Those skilled in the art will recognize that the boundaries betweenlogic circuit blocks are merely illustrative and that alternativeembodiments may merge logic circuit blocks or circuit elements or imposean alternate decomposition of functionality upon various logic circuitblocks or circuit elements. Thus, it is to be understood that thearchitectures depicted herein are merely exemplary, and that in factmany other architectures can be implemented which achieve the samefunctionality.

Any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality can be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermedial components. Likewise, any two components soassociated can also be viewed as being “operably connected,” or“operably coupled,” to each other to achieve the desired functionality.

Furthermore, those skilled in the art will recognize that boundariesbetween the above described operations merely illustrative. The multipleoperations may be combined into a single operation, a single operationmay be distributed in additional operations and operations may beexecuted at least partially overlapping in time. Moreover, alternativeembodiments may include multiple instances of a particular operation,and the order of operations may be altered in various other embodiments.

Also for example, in one embodiment, the illustrated examples may beimplemented as circuitry located on a single integrated circuit orwithin a same device. Alternatively, the examples may be implemented asany number of separate integrated circuits or separate devicesinterconnected with each other in a suitable manner.

Also for example, the examples, or portions thereof, may implemented assoft or code representations of physical circuitry or of logicalrepresentations convertible into physical circuitry, such as in ahardware description language of any appropriate type.

Also, the invention is not limited to physical devices or unitsimplemented in non-programmable hardware but can also be applied inprogrammable devices or units able to perform the desired devicefunctions by operating in accordance with suitable program code, such asmainframes, minicomputers, servers, workstations, personal computers,tablets, notepads, personal digital assistants, electronic games,automotive and other embedded systems, smart phones/cell phones andvarious other wireless devices, commonly denoted in this application as‘computer systems’.

However, other modifications, variations and alternatives are alsopossible. The specifications and drawings are, accordingly, to beregarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word ‘comprising’ does notexclude the presence of other elements or steps then those listed in aclaim. Furthermore, the terms “a” or “an,” as used herein, are definedas one or more than one. Also, the use of introductory phrases such as“at least one” and “one or more” in the claims should not be construedto imply that the introduction of another claim element by theindefinite articles “a” or “an” limits any particular claim containingsuch introduced claim element to inventions containing only one suchelement, even when the same claim includes the introductory phrases “oneor more” or “at least one” and indefinite articles such as “a” or “an.”The same holds true for the use of definite articles. Unless statedotherwise, terms such as “first” and “second” are used to arbitrarilydistinguish between the elements such terms describe. Thus, these termsare not necessarily intended to indicate temporal or otherprioritization of such elements. The mere fact that certain measures arerecited in mutually different claims does not indicate that acombination of these measures cannot be used to advantage.

Unless otherwise stated as incompatible, or the physics or otherwise ofthe embodiments prevent such a combination, the features of thefollowing claims may be integrated together in any suitable andbeneficial arrangement. This is to say that the combination of featuresis not limited by the specific form of claims below, particularly theform of the dependent claims, and as such a selection may be driven byclaim rules in respective jurisdictions rather than actual intendedphysical limitation(s) on claim combinations. For example, reference toanother claim in a dependent claim does not mean only combination withthat claim is envisaged. Instead, a number of claims referencing thesame base claim may be combined together.

The invention claimed is:
 1. Processing logic circuit for use in acomputing system, wherein the processing logic circuit has a StateRetention Power Gating logic circuit having at least two scan chainshaving different lengths and operable to collect state information aboutat least a portion of the processing logic circuit before the at least aportion of the processing logic circuit is placed from a first stateinto a second, different, state, said processing logic circuitcomprising: a memory coupled to the State Retention Power Gating logiccircuit and operable to store a collected state information about the atleast a portion of the processing logic circuit; and a further logiccircuit coupled to the memory and operable to rearrange the collectedstate information data for scan chains shorter than a longest scan chainwithin the at least a portion of the processing logic circuit, to enablevalid return of the collected state information data, for the scanchains shorter than a longest scan chain, to the at least a portion ofthe processing logic circuit when the at least a portion of theprocessing logic circuit returns to the first state.
 2. The processinglogic circuit of claim 1, wherein the second, different, state is astate in which the at least a portion of the processing logic circuit isin a different context or is in a lower power state.
 3. The processinglogic circuit of claim 1, wherein the further logic circuit coupled tothe memory comprises a processing unit within a same or another portionof the processing logic circuit that is to be placed into the second,different, state.
 4. The processing logic circuit of claim 3, whereinthe processing unit is a central processing unit, CPU, within theprocessing logic circuit.
 5. The processing logic circuit of claim 1,wherein to rearrange the collected state data for scan chains shorterthan the longest scan chain comprises moving invalid state datacollected during a SRPG state data storing process from one end of thedata structure comprising the state data to another end of the datastructure.
 6. The processing logic circuit of claim 1, wherein thecollected state information data is stored in a FIFO memory datastructure and the stored collected state information data is rearrangedby placing invalid state information data for a shorter scan chain at anend of the FIFO memory that is loaded first back into the at least aportion of the processing logic circuit.
 7. The processing logic circuitof claim 1, wherein the processing logic circuit is a processor for acomputing system or a System on Chip.
 8. The processing logic circuit ofclaim 1, wherein the memory coupled to the State Retention Power Gatinglogic circuit is part of the at least a portion of the processing logiccircuit to be placed from a first state into a second different state,and the processing logic circuit further comprises further logic circuitto reset the at least a portion of the processing logic circuitcontaining the memory.
 9. The processing logic circuit of claim 1,wherein the at least a portion of the processing logic circuit comprisesany SRPG enabled modules or portions of the processing logic circuit.10. A method of scan chain data management in processing logic circuit,wherein the processing logic circuit has State Retention Power Gatinglogic circuit having at least two scan chains having different lengthsand operable to collect state information about at least a portion ofthe processing logic circuit before the at least a portion of theprocessing logic circuit is placed from a first state into a second,different, state, said method comprising: collecting state informationabout at least a portion of the processing logic circuit before the atleast a portion of the processing logic circuit is placed from a firststate to a second, different, state; and rearranging the collected stateinformation data for the scan chains shorter than a longest scan chain,to enable valid return of the collected state information data for theshorter scan chains to the at least a portion of the processing logiccircuit when the at least a portion of the processing logic circuitreturns to the first state.
 11. The method of claim 10, wherein thesecond, different, state is a state in which the at least a portion ofthe processing logic circuit is in a different context or is in a lowerpower state.
 12. The method of claim 10, further comprising using aprocessing unit within a same or another portion of the processing logiccircuit that is to be placed into the second, different, state.
 13. Themethod of claim 12, further comprising using a processing unit that is amain central processing unit, CPU, or another CPU within the processinglogic circuit.
 14. The method of claim 10, wherein rearranging thecollected state data for scan chains shorter than the longest scan chaincomprises moving invalid data collected during a SRPG state data storingprocess from one end of the data structure comprising the state data toanother end of the data structure.
 15. The method of claim 10 furthercomprising storing the collected state information data in a FIFO memorydata structure and rearranging the stored collected state informationdata by placing invalid state information data for a shorter scan chainat an end of the FIFO memory that is loaded first back into the at leasta portion of the processing logic circuit.
 16. The method of claim 10,further comprising collecting state information using a memory coupledto the State Retention Power Gating logic circuit that is part of the atleast a portion of the processing logic circuit to be placed from afirst state into a second different state; and resetting the at least aportion of the processing logic circuit prior to or at a same time asrearranging the data.
 17. The method of claim 10, further comprisingapplying the method to any SRPG enabled modules or portions of theprocessing logic circuit.